1. Field of the Invention
The present invention relates to cables and, in particular, to cables incorporating tapes which provide water-blocking and flame-retarding characteristics to the cables.
2. Description of the Related Art
Many products, such as telecommunications and power cables, for instance, typically are provided with one or more forms of water-blocking protection, i.e. waterproof outer jackets, water-blocking powders and yarns, etc. Generally, such water-blocking protection is intended to reduce or eliminate the possibility of water entering the product so as to reduce the potential of water damaging the product. For example, once water enters a telecommunications cable, such as through a splice closure of the cable, freezing of the water can induce microbending in the optical fibers of the cable, potentially resulting in fiber degradation or increased signal loss of the cable.
Heretofore, some prior art cables have incorporated water-blocking tape in order to prevent water penetration into and migration through the cables. Examples of such prior art cables are described in U.S. Pat. No. 4,867,526, issued to Arroyo, for instance. In the cables described in U.S. Pat. No. 4,867,526, water-blocking tape is disposed between the transmission media and the outer jacket of the cable, thereby forming a water-blocking barrier around the transmission media, i.e. optical fibers. The water-blocking tape incorporates superabsorbent materials, e.g. superabsorbent polymers (SAPs), which can absorb up to about one thousand (1000) times their weight in distilled water. The SAPs are provided in a loading of approximately 3.8-6.22 g/ft.sup.2, which results in a tape that weighs approximately 10-80% more than the substrate of the tape. Upon contact with water, the SAPs of the water-blocking tape absorb the water and swell, thereby preventing migration of the water through the cable. Additionally, the swollen SAPs form a physical barrier which can prevent more water from entering the cable.
In some applications, it is desirable to provide tapes which incorporate both water-blocking and flame-retarding characteristics. Heretofore, a prior art solution to attain the characteristics of water-blocking and flame-retarding has been to add flame-retardants to the SAPs of the tapes. However, adding flame-retardants to the SAPs oftentimes results in a tape which has reduced water-blocking characteristics as compared to the tape without the flame-retardants. Primarily, this is due to the chemical properties of the prior art flame-retardants which, typically, are salts or ionic compounds and are known to reduce the swelling of water-blocking materials. Generally, as more prior art flame-retardants are added to SAPs in an effort to improve the flame-retarding characteristics, the greater the water-blocking capacity of the SAPs is reduced. Frequently, the extent of reduction in water-blocking capacity of SAPs due to the incorporation of prior art flame-retardants can render the SAPs incapable of preventing water penetration.
Therefore, there is a need to provide improved cables and tapes which address these and other shortcomings of the prior art.